The present invention relates to the recording, storage and reading of magnetic data, and more particularly to rotatable magnetic discs used in cooperation with magnetic transducing heads and having at least portions of their data recording surfaces textured for contact with the transducing heads.
Magnetic discs and disc drives are well known for their utility in storing data in magnetizable form. They typically employ one or more discs rotated on central axis, in combination with data transducing heads positioned at close proximity to the recording surfaces of the discs and moved generally radially with respect to the discs. Generally these devices are of two kinds. The first uses flexible or "floppy" discs, with associated transducing heads contacting the recording surfaces at all times. The second type employs rigid discs rotated at much higher speeds than flexible discs. The transducing heads, during reading and recording operations, are maintained at a controlled distance from the recording surface, supported on a "bearing" of air as the disc rotates. The transducing heads contact their associated recording surfaces whenever the discs are stationary, when they accelerate from a stop, and during deceleration just before coming to a complete stop.
While all such magnetic recording devices experience at least some wear, the problem is particularly serious for the rigid discs and associated heads. This is due in part to the stricter design tolerances associated with rigid discs and heads, arising from the ever-present challenge of increasing the density of data stored on disc recording surfaces. It is considered desirable during reading and recording operations to maintain each transducing head as close to its associated recording surface as possible, i.e. to minimize the "flying" height of the head. A smooth, specular recording surface is thus preferred, as well as a smooth opposing surface of the associated transducing head. This permits closer proximity of the head to the disc, and more predictable and consistent behavior of the air bearing supporting the head.
However, if the head surface and recording surface are too flat, the precision match of these surfaces give rise to excessive stiction and friction during the start up and stopping of the disc, causing wear to the head and recording surface which eventually can lead to a head crash.
In recognition of this difficulty, the recording surfaces of magnetic discs often are intentionally roughened to reduce the head/disc friction. In particular, rigid disc can be formed with an aluminum substrate polished flat and plated with a nickel-phosphorous alloy. The alloy is polished to a substantially specular finish, e.g. to a roughness of less than 0.1 microinch. The disc is then rotated between opposed pressure pads or rollers which support a cloth or paper coated with silicon carbide (SiC) or other suitable grit of a size predetermined to yield roughness peaks of about one microinch. Peaks thus created tend to be jagged and have sharp edges, and are difficult to control in size, form and location as these factors depend largely upon the nature of the grit and the direction which the disc moves relative to the pressure pads or rollers.
In U.S. Pat. No. 4,698,251 (Fukuda et al), a polishing paper is applied to magnetic discs to form circumferential scratch marks having depths from 0.0002 to 0.1 microns into the nickel-phosphorous alloy layer coated onto an aluminum substrate. Following polishing, a chromium layer and a cobalt nickel magnetic layer are formed on the disc. In another embodiment, a nickel-phosphorous layer is deposited onto an aluminum substrate, scratches are formed in the nickel-phosphorous layer, then a cobalt-phosphorous magnetic layer is deposited on the nickel-phosphorous layer.
As an alternative to using grit paper or cloth, U.S. Pat. No. 4,326,229 (Yanagisawa) discloses a protective film layer for covering a smooth recording medium layer of a magnetic disc. To form the protective coating, a solvent is applied in a spin coating process to form a film with radially extending sinusoidal jogs or undulations to increase surface roughness, which is said to reduce head wear.
While each of the above approaches can be satisfactory under certain circumstances, all require compromise between the competing goals of reduced head/disc friction and minimum transducer flying height, and none affords the desired amount of control over surface texture.
Therefore, it is an object of the present invention to provide a magnetic recording medium in which peaks and indentations forming surface roughness are of a controlled size and shape for substantially reduced flying height, improved recording density, and improved transducing head and disc wear characteristics.
Another object of the invention is to provide a process for controlling the texture of a strictly delineated portion of a magnetic disc recording surface while providing a specular finish on the remainder of the recording surface.
Another object is to provide a process for controllably forming the surface texture of a magnetic data recording disc through control of the size and spacing between generally circular individual discontinuities providing texture.
Yet another object is to provide a magnetic recording disc with designated surface areas for contact with data transducing heads, which designated areas exhibit substantially enhanced friction and wear characteristics.